The primary goals of effective cocaine addiction treatment are accelerating extinction and preventing relapse of drug seeking behavior. Despite extensive research, no treatments have clearly shown to be effective towards these ends. Therefore, better understanding of molecular processes that facilitate extinction and prevent reinstatement is a critical research goal. In this proposal, I provide a multidisciplinary plan to identify the molecular mechanisms that regulate the extinction and reinstatement of cocaine-seeking behaviors using cocaine-induced conditioned place preference (CPP), a widely used preclinical model of reward-related learning and memory. My central hypothesis is that activation of Cav1.2 L-type Ca2+ channel in the prefrontal cortex mediates extinction of cocaine conditioned place preference through regulation of the histone deacetylase HDAC5. If validated, this hypothesis would identify Cav1.2 as a promising target for novel treatments for cocaine addiction. First, I will use viral mediated gene transfer to create focal knockdown or over-expression of Cav1.2 in mouse prefrontal cortex, one of the brain regions that is critically involved in extinction learning. The viruses will be administered so that the change in Cav1.2 expression will coincide with the start of extinction training. These mice will be characterized in the acquisition, extinction and reinstatement of cocaine CPP. The performance of the Cav1.2 knockdown, Cav1.2 over-expressing and control mice, (which have basal levels of Cav1.2) in cocaine CPP extinction and reinstatement will be compared. The differences between these cohorts of mice will address the hypothesis that Cav1.2 L-type Ca2+ channels in the prefrontal cortex mediate extinction and reinstatement of cocaine CPP. Next, I will examine the molecular consequences of Cav1.2 manipulation in the prefrontal cortex. When HDAC5 is exported to the cytoplasm from the nucleus, there is increased activation of gene expression which is thought to mediate extinction. Therefore, I will dissect the prefrontal cortex from the behaviorally characterized mice and perform nuclear and cytoplasmic fractionation. I will then use immunoblotting to measure the amount of HDAC5, phospho-HDAC5 and phosphorylated CaMKII, a protein which acts on HDAC5, in these fractions. Also in the behaviorally characterized mice, I will use high resolution dual labeling electron microscopy to quantify HDAC5 or phospho-HDAC5 in neurons that are co-labeled with GFP to further validate the molecular consequences of Cav1.2 manipulation using a different method. I will also use this method to study the molecular consequences of Cav1.2 manipulation in the PFC on chromatin regulation in GABAergic versus glutamatergic cell types. Since these analyses will be performed on behaviorally characterized mice, it will allow for association of molecular and behavioral consequences of prefrontal cortical Cav1.2 manipulations.